During the Patch 1.1.1 Campfire Chat, developer Joe Piepiora confirmed once patch 1.1.1 goes live, starting at level 35, Dungeon Bosses are guaranteed to drop a Legendary item. This also extends to completing Legion Events.
Finally, since The Butcher counts as a boss, he too will be guaranteed to drop a Legendary item. FRESH LOOT! Patch 1.1.1 Unofficial Patch Notes Before level 35, there is still the chance that a Legendary item will drop from any of the formerly mentioned activities.
However, now you will always receive one after reaching that specified level. This extends to all difficulties, and should make things that were previously perhaps slightly unfulfilling to complete a little more exciting.
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